Abstract

Gene therapy is an attractive treatment option for diseases of genetic origin, including several cancers and cardiovascular diseases. While viruses are effective vectors for delivering exogenous genes to cells, concerns related to insertional mutagenesis, immunogenicity, lack of tropism, decay and high production costs necessitate the discovery of non-viral methods. Significant efforts have been focused on cationic polymers as non-viral alternatives for gene delivery. Recent studies have employed combinatorial syntheses and parallel screening methods for enhancing the efficacy of gene delivery, biocompatibility of the delivery vehicle, and overcoming cellular level barriers as they relate to polymer-mediated transgene uptake, transport, transcription, and expression. This review summarizes and discusses recent advances in combinatorial syntheses and parallel screening of cationic polymer libraries for the discovery of efficient and safe gene delivery systems.

Diacrylate esters and amine monomers to synthesize the lead poly-beta-amino esters, C32, JJ28 and C28, as demonstrated by Anderson et al. [33]. Reprinted from Ref. [33] by the permission of Nature Publishing Group.

Synthesis procedures and the structures of α-CD-oligoethyleneimine (OEI) star polymers as described by Yang et al.[55]. The hydroxyl groups of six glucose subunits of α-CD were activated using 1,1’-carbonyldiimidazole (CDI) following the reactions with multiple OEI of different lengths to produce the α-CD-OEI polymers. Adopted from Ref. [55] by permission from Elsevier.

Schematic representation of chitosan grafted pEI copolymer (CS-g-pEI) as proposed by Jiang et al. [62]. The reaction was carried out in two steps in which periodate-oxidized chitosan was prepared in the first step followed by an imine reaction with an amine group of pEI. Adopted from Ref. [62] with permission from Elsevier.

Synthetic scheme of various oligoamine conjugated cationic schizophyllan (SPG) polysaccharaides as shown by Nagasaki et al. [83]. The figure is reprinted with permission from American Chemical Society.

(i) Comaprison of transfection efficiency of lead polymers of a diglycidyl ether polyamine library representing their relative luciferase gene expression in PC3-PSMA prostate cancer cells [85]. The polymer, 1,4C-1,4 Bis demonstarted 80-fold higher luciferase expression than that of pEI-25. (ii) Cytotoxicity of 1,4 C-1,4 Bis, pEI-25, and their polyplexes in PC3-PSMA cells at different polymer DNA weight ratios. 1,4C-1,4 Bis polymer had lower toxicity than pEI-25 [85]. Figures are reprinted by permission of Americal Chemical Society. (iii) Subcellular localization of polymer:DNA complexes are important for diffusion of DNA inside nucleus as a necessary step of efficient gene expression [86]. Confocal microscopic images of fluorescein labeled DNA and polymer complexes showed their distribution throughout the cytoplasm in PC3 prostate cancer cells (left) which, in contrast, displayed their accumulation in single spots inside the cytoplasm of a sub-cell line, PC3-PSMA cells (right). The figures are reproduced with permission from Elsevier. (iv) Modulation of the polyplex trafficking behavior using a histone deacetylase 6 inhibitor, tubacin diffused the polyplexes all around the cell nuclei (right) rather transported them to one single spot on top of the nuclei (left) [86]. Following tubcain treatments and simultaneous transfection of both (v) PC3-PSMA and (vi) PC3 cells using luciferase DNA performed 40 and 35-fold higher luciferase gene expression, rescpectively compared to the untreated control cells [86]. Reprinted with permission from Elsevier.